Study On Physical And Catalytic Properties Of Rhodium-based Metal Clusters By Density Functional Theory

Density functional theory（DFT） is used in this thesis to study:（1） The ground state geometries and electronic properties of Rh_n-1X（n=2-5; X=3d, 4d atoms） and Rh_n-1X-Y（Y=H, O and N） clusters are systematically investigated.（2） The ground state geometries and electronic properties of Rhn（n=2-5） clusters with the adsorption of small molecules are systematically investigated. The main conclusions are as follows:（1） The ground state geometries and electronic properties of Rh_n-1X（n=2-5; X=3d, 4d atoms） and Rh_n-1X-Y（Y=H, O and N） clusters are systematically investigated by using density functional theory calculations. As compared to that of pure Rhn clusters, the lowest-energy geometries of Rh_n-1X clusters have different degree of distortion, which are especially obvious in n=5. The magnetic moments of the mixed clusters with doping Mn and Fe are obviously enhanced, which are mainly derived from the strong spin splitting of d electrons on the doped atoms. By analyzing the adsorption of H, O and N on the mixed clusters, H atom is found to adsorb on the top or bridge site rather than the hollow site, but the adsorption sites of O and N are much more complex. The adsorption energies of O and N are all larger than that of H. The adsorption energies of O are generally stronger than that of N, but in a few cases the opposite result can be found, which can be attributed to the significant difference in the interaction between the s-p electrons of O, N and the d electrons of the doped clusters. The adsorption energies of O on the clusters with doping the early 3d and 4d transition metal atoms are significantly stronger than that with doping the late 3d and 4d transition metal atoms.（2） The ground state geometric structures and electronic properties of Rhn（n=2-5） clusters adsorbed small molecules（H₂, O₂, N2, NO, CO, NO₂, CO₂） are systematically investigated by using the density functional theory calculations. The results show that: N2, NO, CO and CO₂ can be adsorbed on the surface of Rh clusters through physical adsorption; H₂ and NO₂ can be adsorbed on the surface of Rh clusters through chemical adsorption; The adsorption of O₂ on the surface of Rhn is strongly correlated with the parity of the number of Rh atoms: O₂ is chemically adsorbed on the Rhn clusters with odd number of Rh atoms, while O₂ is physically adsorbed on the Rhn clusters with even number of Rh atoms. For the physical adsorption of these small molecules on the surfaces of Rhn, the order of the adsorption energy from strong to weak is NO >（CO≈NO₂≈O₂） >（CO₂≈N2） > H₂.